html页面：

<html>
<head>
    <meta http-equiv="content-type" content="text/html;charset=utf-8" />
    <script type="text/javascript" src="jquery-1.8.2.min.js"></script>
    <script type="text/javascript">
        $(function(){
            $("#send").click(function(){
                var cont = $("input").serialize();
                $.ajax({
                    url:'ab.php',
                    type:'post',
                    dataType:'json',
                    data:cont,
                    success:function(data){
                        var str = data.username + data.age + data.job;
                        $("#result").html(str);
                    }
                });
            });
        });
    </script>
</head>
<body>
<div id="result">一会看显示结果</div>
<form id="my" action="" method="post">
    <p><span>姓名：</span> <input type="text" name="username" /></p>
    <p><span>年龄：</span><input type="text" name="age" /></p>
    <p><span>工作：</span><input type="text" name="job" /></p>
</form>
<button id="send">提交</button>
</body>
</html>

/*******************************************/

php页面：

<?php
header("Content-type:text/html;charset=utf-8");
$username = $_POST['username'];
$age = $_POST['age'];
$job = $_POST['job'];
$json_arr = array("username"=>$username,"age"=>$age,"job"=>$job);
$json_obj = json_encode($json_arr);
echo $json_obj;
?>

使用post方式

<script type="text/javascript">
    $(function(){
        $("#send").click(function(){
            var cont = {username:$("input")[0].value,age:$("input")[1].value,job:$("input")[2].value};
            var url = 'ab.php';
            $.post(url,cont,function(data){
                var res = eval("(" + data + ")");//转为Object对象
                var str = res.username + res.age + res.job;
                $("#result").html(str);
            });
        });
    });
</script>